In a particular charge coupled device (CCD) imager, signal charge representative of incident radiation is accumulated in any array of pixels over an image area. Following an integration period, signal charge is transferred to an output register by applying appropriate clocking pulses to control electrodes. The signal charge is then read out from the output register and applied to a charge detection circuit to produce a voltage. The voltage is representative of the signal charge and hence the intensity of incident radiation.
A known CCD arrangement is shown schematically in FIG. 1A and comprises an image area 10 constituted by an array of pixels 12 arranged to receive incident radiation from an image scene. The incident radiation liberates electrons within the semiconductor structure of the CCD, the number of electrons liberated being related to the level of radiation incident on that pixel. After a defined integration period, the charge accumulated in each pixel is sequentially moved by application of clocking pulses to the pixel away from one row to the next as shown by the arrow A. The rows are successively clocked into a serial register 14 which itself is clocked in the direction indicated by arrow B. In this way, charge is clocked from each pixel, down through the pixel array and to an output circuit 16 by the serial register 14.